U.S. patent application number 13/691088 was filed with the patent office on 2014-06-05 for dual-mode, ac/dc power converter with power factor correction.
This patent application is currently assigned to ATMEL Corporation. The applicant listed for this patent is Sean S. Chen, Dilip Sangam, Hong Zhang. Invention is credited to Sean S. Chen, Dilip Sangam, Hong Zhang.
Application Number | 20140153291 13/691088 |
Document ID | / |
Family ID | 50825302 |
Filed Date | 2014-06-05 |
United States Patent
Application |
20140153291 |
Kind Code |
A1 |
Zhang; Hong ; et
al. |
June 5, 2014 |
DUAL-MODE, AC/DC POWER CONVERTER WITH POWER FACTOR CORRECTION
Abstract
A dual-mode circuit for the control of an AC/DC power converter
is disclosed. An example dual-mode controller circuit generates a
waveform that drives a switch on or off and controls the power
converter. The controller circuit in addition to power factor
correction (PFC) circuitry includes a critical conducting mode
(CrM) module as well as a discontinuous conducting mode (DCM)
module configured to generate waveforms adapted for CrM and DCM
operation of a power converter. The circuit includes a node for
receiving a feedback signal of a voltage or a current. Based on the
received signal, one of the modules is selected at a time to supply
the waveform at the output of the dual-mode controller. An example
of the output waveform is a series of pulses that are configured to
drive the switch that controls the transfer of power between input
and output of the power converter.
Inventors: |
Zhang; Hong; (Mountain View,
CA) ; Chen; Sean S.; (Sunnyvale, CA) ; Sangam;
Dilip; (Saratoga, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Zhang; Hong
Chen; Sean S.
Sangam; Dilip |
Mountain View
Sunnyvale
Saratoga |
CA
CA
CA |
US
US
US |
|
|
Assignee: |
ATMEL Corporation
San Jose
CA
|
Family ID: |
50825302 |
Appl. No.: |
13/691088 |
Filed: |
November 30, 2012 |
Current U.S.
Class: |
363/21.01 ;
327/109 |
Current CPC
Class: |
H02M 1/4258 20130101;
H02M 3/33507 20130101; H05B 45/37 20200101; Y02B 70/10 20130101;
Y02B 70/126 20130101 |
Class at
Publication: |
363/21.01 ;
327/109 |
International
Class: |
H03K 3/00 20060101
H03K003/00; H02M 3/335 20060101 H02M003/335 |
Claims
1. A dual-mode controller circuit comprising: an output (GATE) node
configured to generate an output waveform for driving a switch; an
integrator module adapted to receive a feedback signal of a voltage
or a current and configured to generate a criterion voltage; a
critical conducting mode (CrM) module adapted to receive the
criterion voltage and configured to generate a first output
waveform; a discontinuous conducting mode (DCM) module adapted to
receive the criterion voltage and configured to generate a second
output waveform; and a selector coupled to the integrator and the
CrM and the DCM modules, wherein the selector is adapted to receive
the criterion voltage, and wherein based on the criterion voltage
the selector is configured to select one of the CrM or the DCM
modules, and wherein an output waveform of the selected module is
coupled to the GATE node.
2. The circuit of claim 1, wherein the CrM module is coupled to the
integrator module, and wherein the first output waveform is
adjusted by the criterion voltage and is configured for a CrM
operation of a power converter.
3. The circuit of claim 1, wherein the DCM module is coupled to the
integrator module, and wherein the second output waveform is
adjusted by the criterion voltage and is configured for a DCM
operation of a power converter.
4. The circuit of claim 1, further comprising: a threshold voltage
coupled to the selector, wherein the selection of one of CrM or DCM
modules includes comparing the criterion voltage with the threshold
voltage, and wherein the selection includes a curve with
hysteresis.
5. The circuit of claim 1, wherein the GATE node is coupled to a
switch and drives the switch.
6. The circuit of claim 1, wherein the circuit is a part of an
integrated circuit incorporated in a chip.
7. The circuit of claim 6, wherein the circuit is added to a chip
including a power factor correction circuitry.
8. The circuit of claim 1, wherein the first output waveform and
the second output waveform are a series of pulses.
9. The circuit of claim 1, further comprising: an on-time skew
module, wherein the on-time skew module is configured to modify one
of the first output waveform or the second output waveform, and
wherein the modification includes a change of a time the output
waveform is configured to turn the switch on.
10. The circuit of claim 9, wherein the on-time skew module
modifies the first output waveform and the modification includes an
increase of the time the output waveform is configured to turn the
switch on.
11. The circuit of claim 9, wherein the on-time skew module
modifies the second output waveform and the modification includes a
reduction of the time the output waveform is configured to turn the
switch on.
12. The circuit of claim 1, wherein the dual-mode controller
circuit is coupled to a power converter for output control.
13. The circuit of claim 12, wherein the power converter is an
AC/DC power converter.
14. The circuit of claim 13, wherein the AC/DC power converter is
an isolated AC/DC power converter.
15. The circuit of claim 1, further comprising: a feedback (FB)
node adapted to receive the feedback signal and coupled to a first
input of the integrator, wherein a first reference signal of a
voltage or a current is coupled to a second input of the
integrator, and wherein the criterion voltage is an integral of a
difference of the feedback signal and the first reference signal; a
compensation (COMP) node coupled to the integrator and adapted to
receive the criterion voltage; and a gate driver (DR) module
coupled to the GATE node, coupled to the CrM and the DCM modules,
adapted to receive the output waveform of the selected CrM or DCM
module, and configured to deliver a driving waveform at the GATE
node.
16. The circuit of claim 15, wherein the integrator module is
configured to amplify the difference of the feedback signal and the
first reference signal.
17. The circuit of claim 15, wherein a compensating circuit
including a capacitor is coupled between the COMP node and a
ground.
18. An isolated AC/DC power converter having a primary side ground
and a secondary side ground, the power converter comprising: a
rectifier configured to rectify an alternating input voltage; a
transformer magnetically coupling a primary side and a secondary
side of the power converter, the transformer including: a primary
winding coupled to the rectifier, a secondary winding coupled to an
output load; a dual-mode primary controller having an output (GATE)
node and an input node and configured for: generating a first
output waveform by a critical conducting mode (CrM) module,
generating a second output waveform by a discontinuous conducting
mode (DCM) module, receiving a feedback signal by the input node,
selecting one of the first output waveform or the second output
waveform based on the received feedback signal, and providing the
selected output waveform at the GATE node; a switch coupled to the
GATE node and commanded by the selected output waveform of the
dual-mode primary controller, the switch coupled between the
primary winding of the transformer and a primary side ground and
configured to control the flow of a current in the primary winding
of the transformer; and a secondary controller coupled to the
output load and configured to generate an error voltage and
supplying the error voltage as the feedback signal to the dual-mode
primary controller.
19. The power converter of claim 18, further comprising a secondary
regulation module coupled between the secondary controller and the
dual-mode primary controller and configured to receive one or more
of output parameters from the secondary controller and generate the
feedback signal, the output parameters including: an output current
error, an output voltage error, an output current, and an output
voltage.
20. The power converter of claim 19, further comprising an
auxiliary secondary winding of the transformer coupled to the
secondary regulation module and configured to generate a signal
proportional to the output voltage.
21. The power converter of claim 19, wherein the secondary
controller and the secondary regulation module are optically
coupled.
22. The power converter of claim 18, wherein the feedback signal is
a direct proportional value to one or more output parameters
including: an output current error, an output voltage error, an
output current, and an output voltage.
23. The power converter of claim 18, further comprising: an on-time
skew module in the dual-mode primary controller, wherein the
on-time skew module is configured to modify one of the first output
waveform or the second output waveform, and wherein the
modification includes a change of a time the output waveform is
configured to turn the switch on.
24. The power converter of claim 23, wherein the on-time skew
module of the dual-mode primary controller modifies the first
output waveform and the modification includes an increase of the
time the output waveform is configured to turn the switch on.
25. The power converter of claim 23, wherein the on-time skew
module of the dual-mode primary controller modifies the second
output waveform and the modification includes a reduction of the
time the output waveform is configured to turn the switch on.
26. The power converter of claim 18, wherein the switch is a
transistor.
27. The power converter of claim 18, wherein the rectifier is a
diode bridge.
28. A method of providing a waveform as an output of a dual-mode
controller configured for driving a switch, the method comprising:
receiving a feedback signal of a voltage or a current at an input
node of the dual-mode controller; constructing a criterion voltage
from the received feedback signal; selecting, based on the
criterion voltage, one of a critical conducting mode (CrM) module
or a discontinuous conducting mode (DCM) module; generating, based
on the selected module, one of a first output waveform of the CrM
module or a second output waveform of the DCM module; and
delivering the generated output waveform at an output of the
dual-mode controller, where the method is performed by one of
hardware processors or circuits.
29. The method of claim 28, wherein the output of the dual-mode
controller is coupled to a switch and drives the switch.
30. The method of claim 29, wherein the switch is combined into the
dual-mode controller and the combination is part of an integrated
circuit incorporated in a converter chip.
31. The method of claim 28, wherein constructing the criterion
voltage includes integrating a difference of the received feedback
signal and a first reference signal of a voltage or current.
32. The method of claim 28, wherein selecting includes comparing
the criterion voltage with a threshold voltage, and wherein the
selection includes a curve with hysteresis.
33. The method of claim 28, wherein generating the first output
waveform includes adjusting the first output waveform by the
criterion voltage, and wherein the first output waveform is
configured for a CrM operation of a power converter.
34. The method of claim 28, wherein generating the second output
waveform includes adjusting the second output waveform by the
criterion voltage, and wherein the second output waveform is
configured for a DCM operation of a power converter.
35. The method of claim 28, wherein the received feedback signal is
directly proportional to one or more output parameters including:
an output current error, an output voltage error, an output
current, and an output voltage.
36. The method of claim 28, wherein one of the first output
waveform of the CrM module or the second output waveform of the DCM
module is modified, and wherein the modification includes a change
of a time the output waveform is configured to turn the switch
on.
37. The method of claim 36, wherein the first output waveform is
modified and the modification includes an increase of the time the
output waveform is configured to turn the switch on.
38. The method of claim 36, wherein the second output waveform is
modified and the modification includes a reduction of the time the
output waveform is configured to turn the switch on.
39. The method of claim 28, wherein the first output waveform and
the second output waveform are a series of pulses.
40. The method of claim 28, wherein the dual-mode controller is
coupled to a power converter for output control.
41. The method of claim 40, wherein the power converter is an AC/DC
power converter.
42. The method of claim 41, wherein the AC/DC power converter is an
isolated AC/DC power converter.
43. A method of controlling an isolated AC/DC power converter,
wherein the converter includes a dual-mode primary controller and a
secondary controller, the method comprising: rectifying an
alternating input voltage; applying the rectified voltage to a
primary winding of a transformer, the primary winding being coupled
to a switch and regulated by the switch; driving an output load by
a secondary winding of the transformer, the load coupled to the
secondary controller; generating an error voltage by the secondary
controller; providing the error voltage to the dual-mode primary
controller; based on the error voltage, providing by the dual-mode
primary controller one of a first output waveform generated by a
critical conducting mode (CrM) module, a second output waveform
generated by a discontinuous conducting mode (DCM) module; and
controlling output load parameters by applying the provided output
waveform of the dual-mode primary controller to the switch.
44. The method of claim 43, wherein the error voltage is directly
proportional to one or more output parameters including: an output
current error, an output voltage error, an output current, and an
output voltage.
45. The method of claim 43, wherein one of the first output
waveform or the second output waveform is modified, and wherein the
modification includes a change of a time the output waveform is
configured to turn the switch on.
46. The method of claim 45, wherein the first output waveform is
modified and the modification includes an increase of the time the
output waveform is configured to turn the switch on.
47. The method of claim 45, wherein the second output waveform is
modified and the modification includes a reduction of the time the
output waveform is configured to turn the switch on.
48. A dual-mode controller circuit configured to provide pulses for
driving a switch on or off for controlling an output of a power
converter, the circuit comprising: a feedback (FB) node adapted to
receive a feedback signal of a voltage or a current; a compensation
(COMP) node; an output (GATE) node configured to provide the
pulses; an integrator module including: a first inverting input
node coupled to the FB node of the circuit, a second non-inverting
input node coupled to a first reference signal of a voltage or a
current, and a third output node coupled to the COMP node of the
circuit, wherein a voltage of the output node of the integrator is
an integral of a difference of the signals of the first input and
the second input nodes of the integrator; a comparator module
configured to provide a binary selector (SEL) voltage including: a
first input node coupled to the COMP node of the circuit, a second
input node coupled to a threshold voltage, and a third output node,
wherein the SEL voltage of the output node of the comparator is set
based on comparing a voltage of the first input of the comparator
with a voltage of the second input of the comparator, and wherein a
jump of the SEL voltage includes a curve with hysteresis; a
critical conducting mode (CrM) module configured to generate a
first series of pulses with a first frequency and a first duty
cycle adjusted to a voltage at the COMP node of the circuit and
adapted for a CrM operation of the power converter, the CrM module
including: a first input node coupled to the COMP node of the
circuit, a second input node coupled to the output node of the
comparator module and receiving the SEL voltage, and a third output
node configured to generate the first series of pulses based on the
SEL voltage; a discontinuous conducting mode (DCM) module
configured to generate a second series of pulses with a second
frequency and a second duty cycle adjusted to the voltage at the
COMP node of the circuit and adapted for a DCM operation of the
power converter, the DCM module including: a first input node
coupled to the COMP node of the circuit, a second input node
coupled to the output node of the comparator module and receiving
the SEL voltage, and a third output node configured to generate the
second series of pulses based on the SEL voltage; and a gate driver
(DR) module configured to receive one of the first series of pulses
or the second series of pulses, the DR module including: a first
input node coupled to the output nodes of the CrM and DCM modules
and configured to receive one of the first series of pulses or the
second series of the pulses base on the SEL voltage, a second
output node coupled to the GATE node of the circuit and configured
to provide the received series of pulses at the GATE node of the
circuit.
Description
TECHNICAL FIELD
[0001] This disclosure relates generally to electronics and more
specifically to the output control of AC/DC power converters with
Power Factor Correction (PFC) circuits for driving light emitting
devices, such as Light Emitting Diode (LED).
BACKGROUND
[0002] An AC/DC power converter is used to drive a string of LEDs.
The AC/DC power converter includes a rectifier circuit for
rectifying an AC input voltage into a DC voltage. The isolated
AC/DC power converter includes a transformer and isolates the
output (secondary side) from the input (primary side) of the
converter and therefore separate grounds are used for the input and
the output of the isolated converter circuit. If an inductor
replaces the transformer of the AC/DC power converter, the input
and the output of the converter do not become isolated and share
the same ground. The AC/DC power converter includes PFC circuitry
in the primary controller that controls the input current so that
the input current waveform is in phase with the waveform of the AC
input voltage (e.g., a sine wave). For a good power factor, the
input current waveform will follow the shape and phase of the input
voltage.
[0003] The isolated AC/DC power converters include controllers to
modify the brightness of the string of LEDs. The brightness control
is either implemented from the secondary side of the transformer or
solely from the primary side or the transformer. The method of
controlling the LED lighting form the secondary side is more
accurate and uses a secondary LED controller incorporated in the
secondary side of the transformer and adapted to set the LED
current and measure the LEDs' current and/or voltage. In this
method, there also exists a primary side controller that in
addition to satisfying PFC requirements, receives the secondary
controller's data and causes the necessary changes for the output.
The output load varies a wide range when changing the brightness of
the LEDs. This requires the AC/DC power converter to be able to
operate under full load conditions as well as under light load
conditions.
[0004] Power converters generally incorporate two modes of
operation when dealing with heavy as well as light loads. In
Critical Conduction Mode (CrM) the switching converter initiates a
new switching cycle immediately after the inductor current in the
switching converter goes to zero. In Discontinuous Conduction Mode
(DCM) the switching converter initiates a new switching cycle much
after the inductor current goes to zero and is typically used for
light loads. The CrM is preferred over the DCM because a smaller
switching transistor and a smaller transformer are used. The CrM is
commonly selected for full or heavy loads but the load range for
the CrM is limited and for further light loads the DCM is
preferred.
SUMMARY
[0005] The output control of an AC/DC power converter using a
dual-mode controller is disclosed. An example dual-mode controller
circuit is coupled to a PFC circuitry and provides driving
waveforms for turning a switch on or off in the power converter.
The circuit includes two modules for creating the driving
waveforms. The first module is a CrM module that is configured to
generate a waveform adapted for the power converter to operate
under CrM and the second one is a DCM module that is configured to
generate a waveform adapted for the power converter to operate
under DCM. The controller circuit includes a feedback node for
receiving a feedback signal in the form of a voltage or current. A
criterion voltage is generated from the feedback signal and used to
select one of the CrM or the DCM modules to provide the waveform at
the output of the circuit. The criterion voltage, which is a
measure of the error, is also coupled to the inputs of the CrM and
DCM modules and is used to adjust the waveforms generated by each
module. Finally the output of the selected CrM or DCM module is
delivered at the output of the dual-mode PFC controller.
[0006] In another aspect, an example isolated AC/DC power converter
circuit includes a primary side and a secondary side inductively
coupled through a transformer, and has different grounds for the
primary and the secondary sides. The power converter also includes
a dual-mode primary controller with the PFC circuitry and a
secondary controller at the output of the power converter that
provides an output error signal. A rectifying circuit receives an
alternating input voltage and produces a rectified voltage. The
rectified voltage is coupled to the primary side of the transformer
where the primary side is coupled through a switch to the primary
side ground. The secondary side of the transformer is coupled to an
output load. The dual-mode primary controller circuit receives the
error signal from the secondary controller and based on the error,
provides the output waveform of one of the CrM or the DCM modules
at its output to turn the switch on and off, and control the follow
of current through the primary of the transformer.
[0007] An example method is the delivering of a waveform by a
dual-mode controller to turn a switch on and off. The controller is
configured to generate two different output waveforms. The first
output waveform is designed for operating a power converter in CrM
and the second output waveform is designed for operating a power
converter in DCM. The circuit receives a feedback signal in the
form of a voltage or current and constructs a criterion voltage
from the feedback signal. Based on the criterion voltage one of the
CrM or DCM modules is selected for generating the output waveform
to be delivered at the output of the controller.
[0008] Another example method is controlling an isolated AC/DC
power converter. An alternating input voltage is rectified and
applied to the primary of the transformer. The primary side is
controlled by a dual-mode primary controller that generates either
a waveform adapted for CrM operation of a power converter or
another waveform adapted for DCM operation of a power converter.
The primary controller provides the waveform to a switch where the
switch is also coupled to the primary side of the transformer. The
secondary side of the transformer drives the output load and,
through a secondary controller, provides an output error signal to
the primary controller. The primary controller uses this error
signal to generate a criterion voltage and based on the criterion
voltage, diverts one of the output waveforms of the CrM or the DCM
modules to the switch and controls the amount of energy that is
transferred from the primary side to the secondary side.
[0009] Particular implementations of a PFC controller circuit that
integrates both CrM and DCM modes of operation into one circuit can
operate under heavy output loads as well as light output loads. The
AC/DC power converter that incorporates this circuit supports a
wide load range, utilizing the CrM for heavy loads and the DCM for
light loads while smoothly transitioning between the modes. As an
example, the controller circuit is implemented in an integrated
circuit chip and controls the lighting of a LED diode string.
Another implementation of the controller circuit includes an
on-time skew module. The on-time skew module modifies the output
waveform of the CrM module or the DCM module where the modification
includes a change of the time a switch coupled to the output of the
controller circuit is turned on. Utilizing the on-time skew module
increases the dynamic range for the output control.
BRIEF DESCRIPTION OF THE DRAWINS
[0010] FIG. 1 is a circuit diagram of example circuits that are
coupled to an existing PFC circuit to create a dual-mode
controller.
[0011] FIG. 2 is an example circuit diagram of a dual-mode,
isolated AC/DC power converter with a LED string as its load.
[0012] FIG. 3 is an example flow diagram of a method for driving
the controller of an example circuit as in FIG. 1.
[0013] FIG. 4 is an example flow diagram of a method as in FIG. 3
with the additional step of skewing the on-time of the DCM
waveform.
[0014] FIG. 5 is an example flow diagram of a method for
controlling a dual-mode, isolated AC/DC power converter of an
example circuit as in FIG. 2.
[0015] FIG. 6 is an example of a timing diagram of the output
current and the criterion voltage of an AC/DC power converter.
DETAILED DESCRIPTION
[0016] FIG. 1 is an example circuit 100 designed to produce output
waveforms for controlling an AC/DC power converter. An isolated
power converter utilizes a transformer (not shown) between the
input and the output of the power converter. The circuit 100, as
the primary controller, regulates the flow of current in the
primary side of the transformer. The characteristics of the
waveform generated by the primary controller that drives a switch
coupled to the primary of the transformer on or off determines the
amount of energy transferred from the input to the output. The
circuit 100 is also used for AC/DC power converters where the input
and output of the converter are not isolated. The circuit 100 can
be included in any power converter and by modifying the output
waveform of the circuit 100 the output of the converter is
controlled. An example of the output waveform is a series of pulses
where the frequency and the duty cycle are the parameters to
control the flow of energy. As another example is the utilization
of a pulse width modulation (PWM) scheme for the output
waveform.
[0017] The dual-mode circuit 100 includes a CrM module 104 that
produces a first waveform (e.g., a series of pulses) suitable when
the converter is driving a heavy load and a DCM module 106 that
produces a second waveform (e.g., a series of pulses) suitable for
the operation of the power converter under light loads. The modules
104 and 106 are configured to generate waveforms adapted to comply
with PFC requirements. The circuit 100 receives a feedback signal
through its FB node 120. The received error is applied to inverting
input 130 of an integrator 102 where a first reference signal is
also applied to its non-inverting input 132. The difference of the
two inputs of 102 are integrated and delivered to the output 134.
In another example, integrator 102 additionally amplifies the
output. The output 134 is coupled to input 150 of DCM module and
input 180 of CrM module as well as the circuit's COMP node 122 and
also the input 140 of a comparator module 110. The COMP node
voltage establishes a measure for the amount of error as a
criterion voltage that determines which one of the CrM or DCM
modules should be activated and its output to be delivered as the
output of the circuit 100. The criterion voltage is also an
indication of the amount of energy transferred from the primary
side to the secondary side or the energy delivered to the load. The
comparator module 110 includes another input 142 where another
reference voltage as a threshold voltage is supplied for
comparison. The output 144 of the comparator which is coupled to
the input 152 of DCM module as well as the input 182 of CrM module
provides the selector (SEL) voltage that governs which one of the
output 154 of the DCM module or the output 184 of the CrM should
selected to be delivered to the input 170 of the driver DR module
112. The output 172 of the driver 112 is coupled to circuit's GATE
node 124 which constitutes the output of the circuit.
[0018] The GATE output 124 of the circuit 100 is configured to
drive the switch, typically a discrete power MOSFET or BJT
transistor (not shown) of an AC/DC power converter. The driver 112
amplifies the output signal that drives the switch. The comparator
110 has a hysteresis incorporated into it to ensure the stability
of its output 144 and that the forward and backward jumps of its
output voltage are based on a curve with hysteresis such that the
thresholds for forward and backward jumps are different. The
criterion voltage at COMP node 122 which is also applied to the
input 150 of DCM module and input 180 of CrM module ensures that
the selected module is correctly compensating for the error. A
single capacitor 114 or a combination of the capacitor 114 coupled
in series with a resistor (not shown) and coupled between node 122
and ground 116 provides the necessary compensation for the circuit.
In an example, the dual-mode circuit 100 is coupled to a PFC
circuitry and additionally corrects the power factor for each mode
of operation.
[0019] The circuit 100 includes an extra module 108 called on-time
skew that can affect one of the outputs of the CrM or the DCM
module. In this example, the extra module affects the output of the
DCM module and is located between the output of DCM and input of DR
such that output 154 of DCM is coupled to input 160 of module 108
and output 162 of module 108 is coupled to input 170 of the DR
module. This module modifies the DCM generated waveform (e.g.,
pulses), such that the on-time of the waveform is reduced that
leads to a higher criterion voltage at the COMP node 122 when DCM
module is selected which in turn increases the dynamic range of the
AC/DC power converter that uses this circuit. In another example
(not shown) the on-time skew module is located between the CrM
module and the DR module modifies the CrM generated waveform (e.g.,
pulses), such that the on-time of the waveform is increased and the
same effect is achieved. As an example, the elements disclosed in
circuit 100 as well as the PFC circuitry are included in an
integrated circuit chip configured for controlling an AC/DC power
converter.
[0020] FIG. 2 is an example of an isolated AC/DC power converter
circuit 200 that incorporates the dual-mode primary controller
circuit of FIG. 1 as its module 255. The isolated AC/DC power
converter circuit incorporates a transformer 220 that magnetically
couples the primary side 222 with the secondary side 224. The
primary side 222 is part of the input circuit with an input ground
206 and the secondary side 224 is part of the output circuit with
and isolated output ground 234.
[0021] The output of circuit 200 includes the secondary winding 224
of the transformer that is inversely coupled to its primary winding
and is coupled to a diode 230's anode from one side and the
isolated ground 234 from the other side. A load 240 in parallel
with an output capacitor 232 is coupled between the cathode of
diode 230 and the ground 234. The example circuit has a string of
LEDs as its load. Another example of the circuit 200 includes a
secondary side controller 242 coupled to the load. The secondary
controller is configured to measure one or more of the output
parameters including output voltage, output current, or output
current error.
[0022] The input of circuit 200 includes the primary winding 222 of
the transformer that is coupled to the ground 206 through a switch
260 from one side and to the rectifying Bridge 204 from the other
side where the Bridge 204 is supplied through an alternating
current line 202. At initial power up and before the required
voltage is supplied to module 255 through its node 258 to begin
producing the pulses at node 256, the input capacitor 212 is
charged through resistor 210. When the voltage at node 208 reaches
to a point that module 255 starts operating, the switch 260 starts
turning on and off and causes a current to start flowing at the
output side as well as the auxiliary winding 226. The current
produced by the auxiliary winding 226 also charges the input
capacitor 212 through the diode 218 and resistor 216, and during
normal operation of the power converter this current is the main
source to charge capacitor 212 and provide the current at node 258.
A Zener diode 214 coupled in parallel with capacitor 212 clamps the
voltage at node 258. The secondary and auxiliary windings 224 and
226 are inversely coupled to the primary winding 222 and because of
the orientation of the diodes 230 and 216, the current through both
windings 224 and 226 flow when the switch 260 turns off.
[0023] The module 255 incorporated in circuit 200 is an example of
a dual-mode controller circuit displayed in FIG. 1 where its node
254 is coupled to primary side ground 206. The module 255 is
configured to supply the pulses adapted for either CrM or DCM mode
of operation and additionally satisfies PFC requirements and
delivers the pulses at its output node 256 where it turns the
switch 260 on or off. In an example, the signals from the secondary
controller 242 are applied to a Secondary LED Regulation module
270. In this example the signals are the output current error and
output voltage. The module 270 creates a voltage proportional to
its inputs and applies it to FB node 250 of the module 255. The
module 255 utilizes the error and provides a criterion voltage at
COMP node 252. Based on this error criterion, module 255 delivers
one of the waveforms adapted for DCM or CrM and switches between
these waveforms when required by the output load. As displayed in
FIG. 2, a single capacitor 262 or a combination of the capacitor
262 coupled in series with a resistor (not shown) and coupled
between node 252 and ground 206 provides the necessary compensation
for the module.
[0024] Another example of the same circuit 200 includes a module
255 that includes the on-time skew. The on-time skew module affects
the output waveform of one of the CrM module or the DCM module and
modifies the waveform (e.g. pulses) where the modification includes
a change of the time a switch coupled to the module 255 is turned
on. As an example, the on-time skew affects the output of the DCM
module and modifies the pulses such that the on-time of the pulses
are reduced that leads to a higher criterion voltage at the COMP
node 252 when DCM module is selected which in turn increases the
dynamic range of the controller 242 of the AC/DC power
converter.
[0025] The example circuit 200 is an isolated AC/DC power
converter. If an inductor replaces the transformer of the isolated
AC/DC power converter, the input and the output of the converter do
not stay isolated anymore and share the same ground and the same
module 255 can be used for the output control of this new
circuit.
[0026] FIG. 3 is a flow diagram of process 300 implemented on a
controller as the example circuit 100 of FIG. 1 intended for
delivery of a waveform to control a switch for the output control
of a power converter. The controller receives a feedback signal in
step 310 and generates, from the received feedback signal, a
criterion voltage in step 320. In the next steps 330 and based on
the criterion voltage, the controller selects one of the CrM or the
DCM modules. In step 340 and based on the selected module the first
waveform configured for the CrM operation of a power converter or
the second waveform configured for the DCM operation of a power
converter is generated. Delivering the output waveform of the
selected module at the output of the controller is in step 350.
[0027] FIG. 4 is a flow diagram of process 400 implemented on a
controller as the example circuit 100 of FIG. 1 intended for
delivery of a waveform to control a switch for the output control
of a power converter. The steps 410-440 are similar to steps
310-340 of FIG. 3. In step 450 a skewing process modifies the
waveform generated by the selected module where the modification
includes a change of the time the output waveform is configured to
turn the switch on. In step 460 the output waveform of the selected
module is delivered at the output of the controller.
[0028] FIG. 5 is a flow diagram of a process 500 for controlling an
isolated AC/DC power converter utilizing a dual-mode controller
circuit and implemented on an example circuit 200 displayed in FIG.
2. In step 510, at the input of the power converter an alternating
input voltage is rectified. In step 520, the rectified voltage is
applied to the primary side of a transformer where the primary side
of the transformer is also coupled and governed by a switch. The
secondary of the transformer is driving an output load in step 530
where the output load is coupled to a secondary controller. In step
540, an error voltage is generated by the secondary controller and
the error voltage is provided to the dual-mode controller. Based on
the error voltage of step 540, the dual-mode controller at the
primary side generates in step 550 either a waveform adapted for
CrM or a waveform adapted for DCM operation of the power converter.
In step 560, the waveform generated by the primary controller is
applied to the switch noted in step 520.
[0029] In another example, the dual-mode controller of FIG. 2
incorporates the on-time skew module coupled to the DCM module when
controlling the output of an isolated AC/DC power converter. The
graphs in FIG. 6 display an example timing diagram 600 of the
output load's current Iload and also the voltage of the COMP node
(VCOMP) of the dual-mode controller. The graphs are the current of
the LEDs 240 and the voltage of node 252 in FIG. 2. The 1.times. of
Iload refers to the current of a full load. The 1.times. of VCOMP
is the nominal voltage of the COMP node at the full load. In the
region at the left side of the point 665 of VCOMP and its
corresponding point 615 of Iload, the comparator of FIG. 1 selects
the CrM for the operation of the power converter. In this region
the voltage VCOMP and the load current change from 1.times. to an
example of 0.33.times.. This region which gives an example dynamic
range of 3 in CrM mode would be the same whether the on-time skew
module is incorporated or it is not. When the load drops and the
output current goes below or at the example 0.33.times., VCOMP
drops to 0.33.times. and the comparator of FIG. 1 commands to
change CrM to DCM for the operation of the power converter. When
the load further drops and if there is no on-time skew module for
DCM, the load current and the VCOMP further drop the remainder of
the range (not shown).
[0030] The on-time skew block in FIG. 1 skews the on-time and
modifies the waveform generated by the DCM module. In an example
that the DCM generated waveform is a series of pulses, the on-time
skewing reduces the duration of the pulses that turn on the switch
coupled to the output of the dual-mode controller. The points 685
and 690 on the VCOMP graph are related to the situations that the
skewing technique is effective. By purposely reducing the on-time
of the pulses, the transformer of FIG. 2 does not find enough
on-time to regulate to the example values of 0.33.times. for the
load current. The AC/DC converter regulates by itself to point 690
which increases the VCOMP to adjust for the 0.33.times. of load
current. The VCOMP at point 690 for example becomes 0.7.times.
which is higher than 0.33.times. at point 665. In other words the
voltage VCOMP is pushed up to increase the on-time and as the
result to allow more operational range for further load drop. In
the DCM region between point 690 and point 675, when the load
increases, VCOMP increases and when it becomes lx, the comparator
of FIG. 1 selects CrM over DCM. The on-time skewing not affecting
the CrM, VCOMP drops to a point 685 (e.g., 0.67.times.), giving
more room for the load current to further increase in CrM. Thus,
implementing the on-time skew module increases the dynamic range
for the output control of the power converter.
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